1. Field of the Invention
This invention relates in general to testing samples, e.g. water, for contaminants using a purge and trap instrument and more specifically involves a device that allows testing without removal of the sample from the volatile organic analysis vial in which the sample was field-collected.
2. Background of the Invention
It is often desirable to determine the presence and nature of volatile organic compounds, such as contaminants, in water, soil, and sludge. Typically, field samples are collected in glass bottles or vials. A common field sample collection bottle, called a volatile organic analysis (VOA) vial, is shown in cross-sectional view in FIG. 1 of the drawing and is denoted generally as 10. (Note: Vial 10 shown is common except for the spiking port, denoted generally as 80, which will be described in the Detailed Description.) VOA vial 10 generally includes a glass jar 11, a septum 30, and a cap 20. Glass jar 11, commonly of 40 cc or greater, has a top end 12 terminating in a rim 13 surrounding top opening 14. VOA vial top end 12 includes external threads 15 for attachment of cap 20. Cap 20 has a lower end 22 having internal threads 23 for attachment to vial threads 15. Cap top 25 includes an inward flange 26 surrounding bore 28. Septum 30 is a flexible disk that seals between cap flange 26 and vial rim 13 and covers vial top opening 14 to contain the test sample. Preferably, septum 30 is made of inert resilient material that will not interact with the sample, such as an inert elastomer or an elastomer encapsulated in an inert material, such as a solid fluorocarbon such as teflon. A commonly available septum has a bottom layer 32 of teflon, for contacting the sample and a top layer 34 of elastomer for elasticity and resiliency.
VOA vial 10 is completely filled in the field with liquid sample and capped with septum 30 and cap 20 to assure a gas tight fit. No headspace, i.e. air space, is left in the vial because volatiles in the sample would exit into the headspace and be lost upon opening the vial. Septum 30 is flexible and may move inward or expand outward through cap bore 28 to accommodate contractions and expansions of the sample.
The general testing method, called "purge and trap" requires placing a portion of the sample in a special sparging vessel. Sparging vessels typically hold up to 25 cc. After testing, the inexpensive and contaminated VOA vial containing any remaining sample is typically discarded. The test instrument passes high purity gas bubbles through the sample. The high purity gas bubbles collect the organic vapor and carry it to an absorption tube that concentrates the vapor for subsequent thermal desorption and analysis by gas chromatography or spectrum analysis.
Among other requirements, the special sparging vessels must contain an expansion chamber and must form a gas tight seal with the host purge and trap instrument. An expansion chamber is necessary to prevent contamination of the host instrument from liquids, either in the form of liquid, aerosol mist or foam, entering the instrument. Some samples will foam and bubble easily. Liquid entering the instrument contaminates the instrument which then requires many hours to clean out. Also, liquids entering the instrument may cause thousands of dollars of damage to the instrument. For this reason, it is preferable that the expansion chamber be visible to the user and be made of transparent material so that the user can watch for formation of foam and passage of liquid toward the host instrument. A gas tight seal between the sparge vessel and instrument for up to positive pressures of 20 psig is necessary to prevent any purged gas from escaping. Common commercial purge and trap analytical instruments include a pressure fitting that attaches to the output tube of the special sparging vessel with such a gas tight seal.
Testing requirements are becoming ever more stringent. Mercury and lead contaminants are to be measured in parts per billion. This necessitates testing larger samples and exacerbates some problems in the above-described standard.
One problem of the conventional method is that volatiles can be lost each time the sample or a part of the sample is transferred. Another problem is that the special sparging vessels are expensive and, therefore, are commonly re-used. Re-use of sparging vessels requires cleaning after each use and, of course, introduces doubts as to results obtained from future use of a re-used vessels.
Therefore, the applicant has concluded that it would be desirable to have an expansion chamber device that would connect to a common purge and trap compression fitting and allow the common field sampling VOA vial to be used as the sparging vessel. In this way, no volatiles would be lost due to transfer and no costly vessels are discarded or cleaned.
It is further desirable that the device include means for abating the foaming and bubbling problem.
Of course, it is very desirable that the device achieve these effects without adding any major drawbacks to the sparging operation.
Immediately following each purge and trap analysis it is desirable to test the performance of the instrument to determine the validity of the test results. One method of testing the instrument is to "spike" the sample, i.e. inject a known amount of volatile into the sample and analyze the recovered output.
Therefore, it would be additionally desirable if the field sample bottle includes means for spiking the sample.